Remove per-source speed, fix device dirty check, and add frontend caching

Speed is now exclusively controlled via sync clocks — CSS sources no longer
carry their own speed/cycle_speed fields. Streams default to 1.0× when no
clock is assigned. Also fixes false-positive dirty check on the device
settings modal (array reference comparison) and converts several frontend
modules to use DataCache for consistent API response caching.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/templates/modals/sync-clock-editor.html

@@ -39,7 +39,7 @@
                         <button type="button" class="hint-toggle" onclick="toggleHint(this)" title="?" data-i18n-aria-label="aria.hint">?</button>
                     </div>
                     <small class="input-hint" style="display:none" data-i18n="sync_clock.description.hint">Optional notes about this clock's purpose</small>
-                    <textarea id="sync-clock-description" rows="2" data-i18n-placeholder="sync_clock.description.placeholder" placeholder=""></textarea>
+                    <input type="text" id="sync-clock-description" data-i18n-placeholder="sync_clock.description.placeholder" placeholder="">
                 </div>
             </form>
         </div>